First of all, I can't trust what Ronnie says because in his video he talks about going zero carbs and then he's eating chicken cutlets with barbeque sauce which is almost entirely sugar. I don't think a fined tuned diet matters as much when you weigh 350 pounds and on every chemical on earth.
I've spoken to a lot of old timers and the biggest difference between then and now is fat intake -- especially in the form of eggs. Don Howorth said he ate a dozen eggs a day. There was no such thing as too much meat. The Rheo Blair protein was the real supplement of choice among the top guys and they mixed it with cream. Very, very rich food. Low "starches" as they called carbs in those days. My dad was a pro boxer in the 40's-50's and the way to get lean and strong for fighters was very simple -- lay off the starches. No potatoes, no bread, no rice, no beer, no corn, no oatmeal, no cereal. Steak and eggs. Steak and salad. Steak and more steak. When I was a kid in the 70's and the high carb craze was on I would actually argue with him how his trainers were all wrong. Ha! He had the last laugh. They were right.